1. Field of the Invention
The present invention relates to a fuel pressure control apparatus for a cylinder injection type internal combustion engine installed on an automobile or motor vehicle. More particularly, the present invention is concerned with the fuel pressure control apparatus for the cylinder injection type internal combustion engine which apparatus is designed to prevent the failure of engine starting operation ascribable to the actuation failure of a fuel injection valve which may occur when the pressure of fuel (hereinafter referred to as the fuel pressure) increases as the temperature of the internal combustion engine rises after the stoppage of operation thereof, to thereby ensure the restart of engine operation with high reliability without degrading the ordinary engine operation performance.
2. Description of Related Art
In general, in the cylinder injection type internal combustion engine equipped with a fuel injection system for supplying the fuel to the individual engine cylinders by injecting directly the pressurized fuel into the combustion chambers defined within the cylinders through the fuel injection valves, respectively, the temperature of the fuel remaining within a fuel rail of the fuel injection system rises under the action of heat emanated from the engine and the exhaust system thereof after the engine has been stopped (after the stoppage of the motor vehicle) because cooling by the air stream or wind generated by a cooling fan and the running motor vehicle itself is no more available after the engine operation has been stopped.
In that case, the inner space of the fuel rail remains in the hermetically closed state with the capacity thereof unchanged after the stoppage of the engine operation. Consequently, the fuel pressure within the fuel rail increases due to the thermal expansion of the fuel remaining within the fuel rail. In this conjunction, it is noted that the fuel pressure attainable after the stoppage of the engine operation is naturally high when the fuel pressure at the time point the engine was stopped is high.
Such being the circumstances, when the engine operation is to be restarted from the state where a high fuel pressure prevails internally of the fuel rail shortly after the engine operation was stopped, magnitude of the force acting on a valve element of the fuel injection valve will exceed that of the driving or actuating force applied to the valve element for opening the fuel injection valve, as a result of which such situation will be incurred that the fuel injection valve can not normally operate and hence the operation of the internal combustion engine and the motor vehicle may possibly be disabled to restart, giving rise to a great inconvenience.
In particular, in the case of the cylinder injection type internal combustion engine, the fuel pressure is set at a relatively high level. Consequently, the probability of occurrence of the problem brought about by the increase of the fuel pressure within the fuel rail in succession to or after the stoppage of engine operation is remarkably high.
With a view to solving the problem mentioned above for thereby ensuring the successful restart of the engine operation, there has already been proposed such a fuel pressure control apparatus for the cylinder injection type internal combustion engine in which the temperature rise after the stoppage of engine operation is estimated on the basis of the temperature of engine cooling water and the ambient temperature at the time point when the engine operation is stopped. In that case, if the maximum reachable value of the fuel pressure within the fuel rail is expected to exceed a predetermined fuel pressure level or value due to the temperature rise as estimated, the fuel is then injected through the fuel injection valve immediately after the stoppage of the engine operation to thereby allow the fuel pressure within the fuel rail to lower. For more particulars, reference may have to be made to Japanese Patent No. 3289472, for example.
In other words, the conventional fuel pressure control apparatus mentioned above is so arranged that when the maximum reachable value of the fuel pressure within the fuel rail as estimated reaches or exceeds a critical pressure (i.e., pressure beyond which actuation of the fuel injection valve becomes disabled), the fuel injection is continued even after the stoppage of engine operation to thereby lower or reduce the fuel pressure within the fuel rail so that the fuel pressure within the fuel rail does not reach the critical pressure at which the actuation of the fuel injection valve is disabled regardless of the fuel temperature rise within the fuel rail.
As will now be appreciated from the above, with the conventional fuel pressure control apparatus for the cylinder injection type internal combustion engine, the engine operation is continued even after the input of a command of stopping the engine operation by an operator or driver of the motor vehicle when the fuel pressure within the fuel rail is expected to reach or exceed the critical pressure, as is disclosed in Japanese Patent No. 3289472 cited above. Consequently, the intention of the driver to stop the engine operation instantaneously upon his or her manipulation for inputting the engine stoppage command can not be realized, incurring a great inconvenience as a practical matter. In other words, the measures for solving the problem described above lacks practicality.